Weights & Measures
The basic unit of weight used in dealing with gold is the troy
ounce. One troy ounce is equivalent to 20 troy pennyweights.
In the jewelry industry, the common unit of measure is the pennyweight
(dwt.) which is equivalent to 1.555 grams.

The degree of purity of native
gold, bullion (bars or ingots of unrefined gold), and refined
gold is stated in terms of gold content. "Fineness"
defines gold content in parts per thousand. For example, a gold
nugget containing 885 parts of pure gold and 115 parts of other
metals, such as silver and copper, would be considered 885-fine.
"Karat" indicates the proportion of solid gold in an
alloy based on a total of 24 parts. Thus, 14-karat (14K) gold
indicates a composition of 14 parts of gold and 10 parts of other
metals. Incidentally, 14K gold is commonly used in jewelry manufacture.
"Karat" should not be confused with "carat,"
a unit of weight used for precious stones.

Geological & Mining
Background
Gold is relatively scarce in the earth, but it occurs in many
different kinds of rocks and in many different geological environments.
Though scarce, gold is concentrated by geologic processes to
form commercial deposits of two principal types: lode (primary)
deposits and placer (secondary) deposits.

Lode deposits are the targets
for the "hardrock" prospector seeking gold at the site
of its deposition from mineralizing solutions. Geologists have
proposed various hypotheses to explain the source of solutions
from which mineral constituents are precipitated in lode deposits.

One widely accepted hypothesis
proposes that many gold deposits, especially those found in volcanic
and sedimentary rocks, formed from circulating ground waters
driven by heat from bodies of magma (molten rock) intruded into
the Earth's crust within about 2 to 5 miles of the surface. Active
geothermal systems, which are exploited in parts of the United
States for natural hot water and steam, provide a modern analog
for these gold-depositing systems. Most of the water in geothermal
systems originates as rainfall, which moves downward through
fractures and permeable beds in cooler parts of the crust and
is drawn laterally into areas heated by magma, where it is driven
upward through fractures. As the water is superheated, it dissolves
metals from the surrounding rocks. When the heated waters reach
cooler rocks at shallower depths, metallic minerals precipitate
to form veins or blanket-like ore bodies.

Two thirds of the world's supply
comes from South Africa, and 2/3 of USA production is from South
Dakota and Nevada. Other main mining areas are Canada, Russia,
Australia and China. The metal is recovered from its ores by
cyaniding, amalgamating, and smelting processes. Refining is
also frequently done by electrolysis.

Occurrence of gold in the earth's
crust = .005 parts per million

Estimated total mine production
= 160,000+ tonnes since gold was first discovered
[Date of first gold coin = approx. 560 B.C. (minted by Croesus
of Lydia)]

A metric tonne (equals 1,000kg)
of gold has a volume of 51,762 cubic centimeters, equivalent
to a cube with sides of only 37.27cm -- approx. only 1' 3'' !.

In fact, the total amount of
gold in the world is a surprisingly small quantity. Here's how
you can calculate the volume of the total quantity that has ever
been mined.

The annual worldwide production
of gold is approximately 80 million troy ounces per year. There
are 32.15 troy ounces in a kilogram. Gold has a specific gravity
of 19.3, meaning that it is 19.3 times heavier than water. So
gold weighs 19.3 kilograms per liter. A liter is a cube that
measures 10 centimeters (about 4 inches) on a side. Therefore,
the world produces a cube of gold that is about 5.1 meters (about
17 feet) on each side every year. In other words, all of the
gold produced worldwide in one year could approximately fit into
an average living room and garage!

This annual production weighs
2,572,000 kilograms. A recent spot price for gold was $740 U.S.
-- using that number, all of the gold produced in a year is worth
$59.2 billion.

Similarly, it is estimated
that all the gold ever mined in the world (160,000 tonnes as
of 2007), could be placed in a single cube roughly 60 ft. on
a side, with a value of $3.68 trillion.

Gold occurs in sea water to
the extent of 0.1 to 2 mg/ton, depending on the location where
the sample is taken. No method has been found for recovering
gold from sea water profitably.

The name originates from the
Old English Anglo-Saxon word 'geolo' meaning yellow. The Symbol
Origin is from the Latin word 'Aurum' meaning "Glowing Dawn".

Gold is classified as a "Transition
Metal" which are located in Groups 3 - 12 of the Periodic
Table. An Element classified as a Transition Metals is ductile,
malleable, and able to conduct electricity and heat.

Gold is extremely malleable
(the extent to which a material can undergo deformation in compression
before failure). In the annealed state it can be hammered cold
into a translucent wafer 0.000013 cm thick. One ounce of gold
can be beaten into a sheet covering over 9 square metres and
0.000018 cm thick.

Gold is extraordinarily ductile
(degree of extension which takes place before failure of a material
in tension). One ounce can be drawn into 80 km (50 miles) of
thin gold wire (5 microns diameter) to make electrical contacts.

The ability of gold to efficiently
transfer heat and electricity is bettered only by copper and
silver, making it indispensable in electronics for semi-conductors
and connectors in computer technology -- especially because gold
is at the top of the series indicating its high corrosion resistance.
In practise, gold dissolves only in aqua regia (a mixture of
hydrochloric and nitric acids) and in sodium- or potassium- cyanide.
The latter solvent is the basis for the cyanide process that
is used to recover gold from low-grade ore. In everyday use gold
does not tarnish.

Electronic Uses

The resistance to oxidation
of gold has led to its widespread use as thin layers electroplated
on the surface of electrical connectors to ensure a good connection.
Gold-plated connectors are an integral part of plugs and sockets
for cable terminations, integrated circuit sockets and printed
circuit boards. In general, the more sophisticated the equipment
and the greater the need for reliability, the greater the requirement
to exploit the advantages of gold as a material. This means that
in telecommunications, computers, automotive electronics and
defense systems where safety is critical, gold is indispensable.
Gold performs critical functions in computers, communications
equipment, spacecraft, jet aircraft engines, and a host of other
products.

Other Uses

Gold's efficiency as a reflector
of heat and infra-red radiation has led to liquid gold
being used to reduce heat transmissions from aircraft engines
and in the United States' Apollo space program. In the latter,
reflective gold-coated plastic film was wrapped around parts
of the lunar landing module and the moon buggy to protect sensitive
parts from solar radiation.

Recordable compact discs depend
upon gold's high reflectivity. Disc players require a high reflectivity
of the laser beam and the only possible materials are gold, silver
or copper. With the latter two metals, there is the inherent
risk of tarnishing and oxidation. This is not a concern with
gold. The gold surface is deposited on the recordable CDs by
a process called sputtering.

Jewelry consumes around 75%
of all gold produced. Gold for jewelry can be given a range of
hues depending on the metal with which is alloyed (white, red,
blue, green etc.).

· Green gold (a gold/silver
alloy) is used in specialized jewelry while gold alloys with
copper (reddish color) are more widely used for that purpose
(rose gold).

· Colloidal gold is
added to glass to colour it red or purple.

· Gold can be made into
thread and used in embroidery.

· Gold is used in restorative
dentistry especially in tooth restorations such as crowns and
permanent bridges as its slight malleability makes a superior
molar mating surface to other teeth, unlike a harder ceramic
crown.

· Colloidal gold (a
gold nanoparticle) is an intensely colored solution that is currently
studied in many labs for medical, biological and other applications.
It is also the form used as gold paint on ceramics prior to firing.

· Chlorauric acid is
used in photography for toning the silver image.

· Gold(III) chloride
is used as a catalyst in organic chemistry. It is also the usual
starting point for making other gold compounds.

· Gold is used as a
coating enabling biological material to be viewed under a scanning
electron microscope.

· Many competitions
and honors, such as the Olympics and the Nobel Prize, award a
gold medal to the winner.

· Since it is a good
reflector of both infrared and visible light, it is used for
the protective coatings on many artificial satellites and on
astronauts' helmets to prevent blindness from the sun.

· Gold is applied as
a thin film on the windows of large buildings to reflect the
heat of the Sun's rays.

· Gold flake is used
on and in some gourmet sweets and drinks. Called varak (or varaq)
in India. Having no reactivity it adds no taste but is taken
as a delicacy. Some use it as an excuse to create super-expensive
delicacies ($1,000 cocktails). For similar reasons, it is also
used as the basis for some superstitious, over-the-top health
claims. Only the salts and radioisotopes (mentioned above) have
any evidence of medicinal value.

Medical Uses

The claims for the medical
benefits of gold date back many of thousands of years. Many ancient
cultures, such as those in India and Egypt used gold-based medicinal
preparations. Early applications of gold in China were in the
treatment of ailments such as smallpox, skin ulcers and measles.
In Japan, tradition suggests thin gold-foils placed into tea,
sake and food are beneficial to health.

Apart from the obvious use
of gold alloys in dental restorations, there are also a number
of direct applications of gold in medical devices. As with dental
applications, these are related to the excellent biocompatibility
of gold as a material. Applications include wires for pacemakers
and gold plated stents used in the treatment of heart disease.

Gold possesses a high degree
of resistance to bacterial colonization and because of this it
is the material of choice for implants that are at risk of infection,
such as the inner ear. Gold has a long tradition of use in this
application and is considered a very valuable metal in microsurgery
of the ear.

Gold and gold compounds have
also historically been used in drugs for the treatment of a wide
range of ailments. This use of gold compounds in medicine is
called chrysotherapy. The Frenchman Jacques Forestier reported
in 1929 that the use of gold complexes was beneficial in the
treatment of arthritis. Later work after the Second World War
demonstrated conclusively that gold drugs are effective in treating
rheumatoid arthritis patients. Two of the most commonly referred
to gold compounds in such treatments are Myocrisin and Auranofin.

The isotope gold-198, (half-life:
2.7 days) is used in some cancer treatments and for treating
other diseases.

Finally, it should also be
borne in mind that without the reliability that gold provides
in electronic components within medical devices such as pacemakers
and ventilators, many medical treatments would not be as
effective as they are today.

Catalysts

The following reactions have
now been shown to be effectively catalysed by supported gold
catalysts: